Optical system, in particular intraocular lens, contact lens

ABSTRACT

Intraocular lenses, for example intraocular implants, contact lenses and the like. The optical system is made of a material whereof the refractive index varies along at least one given direction, this material being a homogeneous material with variable index according to its chemical composition or by the action of mechanical effects, or a heterogeneous material with different molecular orientations. The invention is useful for making lenses with accommodative sighting.

FIELD OF THE INVENTION

The present invention relates to optical systems, in particular centeredoptical systems such as intraocular lenses, contact lenses, etc.

BACKGROUND OF THE INVENTION

It is known that the human eye is a complex optical system whose role isto transmit to the brain the images arriving thereat. One of theessential components is the lens. The crystalline lens, located behindthe iris, is a transparent gelatinous mass contained in the lens sac.

Opacification of the crystalline lens may occur with increasing age(cataract). All that can be done in that case is to remove the defectivecrystalline lens and replace it with an artificial crystalline lens oran intraocular lens.

The artificial crystalline lenses known to date are essentially made ofacrylic materials, for example polymethyl methacrylate or copolymersthereof, or of silicone derivatives. They have relatively low refractiveindices. For silicones, refractive indices of between 1.41 and 1.46 arecurrently available in the best of cases. For strong corrections, it isthus necessary to use intraocular lenses whose faces have a largecurvature and which are consequently very thick in their optical axis.

In order to obtain the best correction without inducing astigmatismdefects, it is also necessary to introduce the intraocular lens bymaking the smallest possible incision. To do this, flexible materials ofthe largest possible refractive index are sought so as to obtain a verythin intraocular lens.

In a healthy eye the crystalline lens is capable, under the action ofmuscles, the zonulae, which act upon the lens sac, of modifying itsradius of curvature so as to adapt itself to close vision or distantvision.

Replacing the crystalline lens with an intraocular lens no longer allowsaccommodation to take place.

OBJECT OF THE INVENTION

One of the aims of the present invention is to produce an optical systemsuch as an intraocular lens which overcomes the drawbacks of those ofthe prior art.

SUMMARY OF THE INVENTION

More specifically, the subject of the present invention is an opticalsystem, in particular an intraocular lens or contact lens, characterizedin that it is made of a material whose optical refractive index showsvariations in at least one given direction.

According to one characteristic of the invention, the said material is ahomogeneous material whose refractive index is variable as a function ofits chemical composition.

According to another characteristic of the invention, the said materialis a heterogeneous material with molecular orientations which vary indifferent zones.

According to another characteristic of the invention, the said materialis a homogeneous material capable of modifying its optical refractiveindex when it is subjected to the action of external phenomena.

Another application is the production of bifocal contact lenses,allowing a simultaneous correction of two visual defects (for examplemyopia and presbyopia):

either by juxtaposition of two materials, a central material and aperipheral material, of similar nature but of different indices, bymeans of different degrees of grafting onto the same matrix;

or by juxtaposition of two different domains of the same material, thetwo domains having refractive indices that are different by virtue of amolecular orientation;

or by producing a material whose index varies under the effect of amechanical stress, for example the pressure of the eyelids.

BRIEF DESCRIPTION OF THE INVENTION

Other characteristics and advantages of the present invention willbecome apparent in the course of the description which follows, givenwith regard to the drawings attached for illustrative but in no waylimiting purposes, in which:

FIGS. 1 and 2 represent graphs for explaining the variations in theproperties of materials used to produce an optical system such as anintraocular lens according to the invention as a function of thecomposition of these materials, the graph in FIG. 1 showing the changein glass transition temperatures as a function of the content ofsubstituents, and the graph in FIG. 2 showing the change in refractiveindex n as a function of the content of substituents.

DETAILED DESCRIPTION OF THE INVENTION

The optical system such as the intraocular lens according to theinvention is made of a material whose optical refractive index showsvariations in at least one given direction.

In a first embodiment, this material is homogeneous and has a highrefractive index n which varies according to its chemical composition.

Specifically, for a given molecule, the molar refraction R is, to afirst approximation, an additive function of the contributions of thevarious elements present in the molecule. Among the common chemicalgroups, those which have the greatest effects in increasing R are mainlysulfur, the halogens, in particular chlorine, bromine and iodine, andaromatic nuclei.

The refractive index n of the molecule increases as R increases, suchthat it is the molecules containing the elements mentioned above whichhave the largest indices.

Examples

benzene n=1.498

o-dichlorobenzene n=1.551

carbon disulfide n=1.628

diiodomethane n=1.749

Similarly, the addition of groups of high refractive index n to apolymer increases the refractive index of the material.

By way of example, mention will be made of the case of siliconsubstituted with 9-vinylanthracene substituents. The refractive index ofthe material obtained increases as the content of substituentsincreases:

without substituent: n=1.403

with 94% substituents: n=1.690

The glass transition temperatures Tg also increase as the degree ofsubstitution increases due to the rigidity of the aromatic nuclei:

without substituent: Tg=−130° C.

with 94% substituents: Tg=between 10° C. and 20° C.

The process for manufacturing the homogeneous material having a highrefractive index n which is variable according to its chemicalcomposition, and which is necessary for producing an intraocular lensaccording to the invention, comprises the following two steps:

Firstly, groups chosen from those described above, in particulararomatic nuclei whose presence also gives the material obtained thecapacity to filter out ultraviolet radiation, which is an essentialproperty for a high-quality intraocular lens, are fixed onto thepolymers used for the lenses and artificial crystalline lenses, thisfixing being obtained via a flexible portion so as to disrupt thetemperature Tg as little as possible.

Examples

substituent of type [1]:

substituent of type [2]:

Next, the degree of substitution is modified continuously, and thus alsothe refractive index of the material, in order to obtain copolymers witha modulatable proportion of substituted units and of unsubstitutedunits. In the case of silicones, it is necessary to prepare thecopoly(methylhydrogenodimethyl)siloxane of variable compositionbeforehand.

Two examples are given below, one starting with a silicone support, theother starting with an acrylate support, the substituent chosencorresponding to formula [1] above in which n=4, Z=OCO, Y=OC_(m)H_(2m+1)with m=1 and x=1.

In the case of the first example, that with a silicone support, thesubstituent must have a vinyl end bonding group:

Example:

This group can be obtained in two steps: reaction of 4-bromobutene withhydroquinone, followed by esterification with p-methoxybenzoic acid.

The main siloxane chain has a random distribution ofmethylhydrogenosiloxane substitutable units and of dimethylsiloxaneunsubstitutable units in variable proportion. These copolymers areobtained by acid-catalyzed redistribution of dimethylsiloxane unitsintroduced in adequate amount via octamethylcyclotetrasiloxane and ofmethylhydrogenosiloxane units provided byhomopolymethylhydrogenosiloxanes.

The substituent is fixed onto the main chain by hydrosilylation at 60°C. in the presence of a solvent. It is introduced in deficit relative tothe methylhydrogenosiloxane units (from 5% to 15%) in order to allow asubsequent reaction of the excess units during the crosslinking step.

At the end of the hydrosilylation reaction, the polymer is freed ofvirtually all of the solvent by evaporation under vacuum at roomtemperature. It is then mixed with a crosslinking agent, and the rest ofthe solvent is evaporated off under vacuum.

The crosslinking agent is preferably a flexible chain and is terminatedwith two vinyl ends. Its proportion is such that the amount of vinylbonding groups corresponds to the amount of methylhydrogenosiloxaneunits left free.

Example of a crosslinking agent:

CH₂=CH(CH₂)_(p)CH=CH₂ p=2 to 20

CH₂=CH(Si(CH₃)₂O)_(q)CH=CH₂ q=2 to 10

The polymer/crosslinking agent mixture is cast in a mold treated suchthat the material does not stick to the walls. The mold is placed at 60°C. in an oven for several hours in order to obtain a crosslinkedpolymer, which is removed from the mold.

This product can be washed by swelling it with a solvent, in order toremove any unreacted molecules, followed by drying it slowly.

In the second example, that with an acrylate support, the acrylate ormethacrylate monomer, bearing the chosen substituent, must besynthesized:

Example:

with X=H, CH₃

This group can be obtained in four steps: reaction of 4-bromobutanol inwhich the alcohol function has been protected, with hydroquinone;esterification with p-methoxybenzoic acid; deprotection of the alcoholfunction; esterification between this alcohol function and thecarboxylic group of acrylic or methacrylic acid.

A bifunctional monomer containing an acrylate or methacrylate functionat both ends must also be synthesized. It can be obtained according tothe following scheme: reaction of 4-bromobutanol, in which the alcoholfunction has been protected, with hydroxybenzoic acid; esterificationwith the product of the reaction of 4-bromo-butanol, in which thealcohol function has been protected, with hydroquinone; deprotection ofthe alcohol functions; esterification of these alcohol functions withthe carboxylic functions of acrylic or methacrylic acid.

Other bifunctional monomers can be used: ethylene glycol dimethacrylate;triethylene glycol dimethacrylate; tetraethylene glycol dimethacrylate;1,6-hexanediol dimethacrylate; 1,12-dodecanediol dimethacrylate.

The polymerization is initiated by heating or UV irradiation in thepresence of an initiator (for example azobisisobutyronitrile) or by anyother common system (chemical accelerator, microwave irradiation).

The production of crosslinked materials with a variable proportion ofsubstituents is possible by mixing, prior to the polymerizationreaction, one or more unsubstituted monomers (methyl acrylate, methylmethacrylate or hydroxyethyl methacrylate, for example) with the abovemonofunctional and bifunctional monomers in suitable proportion.Hydroxyethyl methacrylate (HEMA) gives the material a hydrophilic natureuntil a degree of hydration of 40% for a homopolymer is obtained. Evenmore hydrophilic comonomers may be combined therewith, such asN-vinylpyrrolidone (VP) for example.

The lenses or crystalline lenses can be obtained either by machining thefinal materials or by carrying out the final step(polymerization/crosslinking) in a mold. When the base monomer hashydrophilic properties, the final material can be swollen in aqueousmedium and become more or less pliable depending on its composition.

Compared with the base acrylates or silicones, the materials thusobtained have properties which allow the preparation of artificialcrystalline lenses, intraocular lenses or contact lenses according tothe invention.

Specifically, their refractive index n and their glass transitiontemperature Tg are higher and vary according to their chemicalcomposition. In particular, they increase as the proportions ofsubstituents increase.

One example of this change is illustrated in FIGS. 1 and 2 for thesilicone materials whose method of synthesis has been given hereinabove.

In this example, the crosslinking agent is an alkyl chain; acrosslinking agent with three different chain lengths corresponding to10, 16 or 22 carbons was studied; three different proportions of thiscrosslinking agent were introduced (5, 10 and 15%). These two parametershave little influence on the change in the refractive index or in theglass transition temperature, as may be seen in FIGS. 1 and 2.

On the other hand, the refractive index increases very rapidly as thecontent of substituents increases, FIG. 2, since with 40% substituents,indices above 1.53 are obtained.

The change in the glass transition temperature, FIG. 1, is slower. Evenwith total substitution, the Tg remains less than room temperature.

The mechanical properties are relatively unaffected by the substituents.For example, the modulus of elasticity under shear (G′) at zerofrequency:

unmodified silicone: G′=10⁵ Pa

silicone with more than 85%

substituents: G′=4×10⁴ Pa

According to a second embodiment, the material of which the intraocularlens according to the invention is made is a heterogeneous material witha high and variable index in the material.

The aromatic substituents proposed above are thermotropic liquidcrystals. They give the polymer bearing them mesomorphic properties,i.e., in particular, molecular orientation properties: within a giventemperature range, these substituents very readily become oriented underthe effect, for example, of a magnetic or electric field. Thisorientation is then “set” by the crosslinking process.

Under the orientation effect as mentioned above, the refractive indexbecomes anisotropic. It is thus possible, by orienting the substituents,to modify the refractive index in a given direction.

According to the present invention, the optical system is obtained fromthe same polymer, for example silicone or acrylate or methacrylate, bypreparing batches with different indices obtained by orienting thesubstituents in different directions.

The orientations can be obtained by placing the substituted polymer (inthe case of silicones) or the various monomers, substituted orunsubstituted (in the case of acrylates) in a weak magnetic field ofabout 1 Tesla or in an electric field, or by a surface treatment of thedevice allowing the material or lens to be manufactured in its finalshape. The crosslinking (in the case of silicones) or thepolymerization/crosslinking (in the case of acrylates) are carried outby heat treatment, for example, under this orientating field.

These batches of identical chemical nature are entirely compatible. Theymay be assembled so as to form lenses or crystalline lenses withdifferent accommodation zones. For example, an intraocular lens may beproduced in two parts: a central optical zone adapted for close visionand a peripheral zone adapted for distant vision.

According to a third embodiment, the material used to produce theoptical system such as the intraocular lens according to the inventionis a homogeneous material of high index which is variable by means of amechanical effect, thereby allowing accommodation.

According to one characteristic of the invention, the material of whichthe optical system is made is a three-dimensional liquid crystal polymerwhose mesomorphic portions can be readily oriented by means of amechanical effect.

It is possible, for example, firstly to prepare crosslinked liquidcrystal polymers without prior orientation of the mesogenic units. Usingthis material, artificial crystalline lenses or intraocular lenses willthen be produced, for example by polymerization/crosslinking in a moldor by machining depending on the properties of the material. The zonulaeexert a mechanical stress which is reflected, via the lens sac, onto thecrystalline lens. This stress exerted by ocular tissue modifies theorientation of the liquid crystal substituents and thus the refractiveindex in the direction of vision. Similarly, in the case of contactlenses, a pressure from the eyelids can produce mechanical deformationsneeded for the molecular reorientation and thus vary the refractiveindex and consequently the power of the lens.

It is also possible to give these materials a pre-orientation of thesubstituents during their production, which preorientation will bemodified under the effect of compressions or stretches transmitted tothe sac via the zonulae.

In order for the material without preorientation of the mesogenic unitsto be transparent, or in order for a preoriented material to remaintransparent after the disorientation, it is placed in isotropic phaseunder the conditions of use. Furthermore, in order to obtain asufficient orientation under stress and thus a significant modificationof the refractive index, it is necessary to carry out the process in atemperature range about 10° C. above the temperature T_(I) at which thesample becomes isotropic. This obligation imposes an upper limit on thedegree of substitution, as illustrated in FIG. 1. In the example chosen,a siloxane modified to about 35% would be entirely suitable for use: itis isotropic at about 35° C. with a refractive index of greater than1.51 (FIG. 1).

In the isotropic phase, the index variation is proportionately greaterthe closer the temperature of use is to T_(I). An example of thedifference in index between two perpendicular directions, Δn, induced bya mechanical stress is given below. The compound chosen corresponds to amethacrylate substituted with various groups of type [2] defined above:

at T_(I)+4° C. Δn=6×10⁻³ for a stress of 5×10⁻² N.mm⁻² Δn=2×10⁻³ for astress of 2×10⁻² N.mm⁻²

at T_(I)+25° C. Δn=1×10⁻³ for a stress of 5×10⁻² N.mm⁻² Δn=0.3×10⁻³ fora stress of 2×10⁻² N.mm⁻²

What is claimed is:
 1. An ophthalmic lens device comprising a materialhaving an optical refractive index varying in at least one direction inresponse to a force being exerted directly on the material by oculartissue, for causing the refractive index to change, wherein saidmaterial comprises at least one polymer onto which is bonded at leastone substituent selected from the group consisting of sulfur, halogensand aromatic nuclei.
 2. An ophthalmic lens device comprising a materialhaving an optical refractive index varying in at least one direction inresponse to a force being exerted directly on the material by oculartissue, for causing the refractive index to change, wherein saidmaterial comprises at least one polymer onto which is bonded at leastone substituent selected from the group consisting of chlorine, bromineand iodine.
 3. The ophthalmic lens according to claim 1, wherein thepolymer is a silicon or a polymer or a copolymer comprising an acrylateor methacrylate monomer.
 4. The ophthalmic lens according to claim 2,wherein the polymer is a silicon or a polymer or a copolymer comprisingan acrylate or methacrylate monomer.
 5. An ophthalmic lens devicecomprising a material having an optical refractive index varying in atleast one direction in response to a force being exerted directly on thematerial by ocular tissue, for causing the refractive index to change,wherein said material comprises at least one mesomorphic compound.
 6. Anophthalmic lens device comprising a material having an opticalrefractive index varying in at least one direction in response to aforce being exerted directly on the material by ocular tissue, forcausing the refractive index to change, wherein said material comprisesa liquid crystal polymer.
 7. The ophthalmic lens device according toclaim 6, wherein said liquid crystal polymer is a three-dimensionalliquid crystal polymer.
 8. The ophthalmic lens device according to claim6, wherein said liquid crystal polymer is a three-dimensional liquidcrystal polymer having mesomorphic portions capable of being oriented bymeans of a mechanical effect.
 9. The ophthalmic lens device according toclaim 1, wherein said material comprises portions capable of beingoriented by means of a mechanical effect.
 10. The ophthalmic lens deviceaccording to claim 2, wherein said material comprises portions capableof being oriented by means of a mechanical effect.
 11. The ophthalmiclens device according to claim 5, wherein said material comprisesportions capable of being oriented by means of a mechanical effect. 12.The ophthalmic lens device according to claim 6, wherein said materialcomprises portions capable of being oriented by means of a mechanicaleffect.
 13. The ophthalmic lens device according to claim 1, whereinsaid material has an optical refractive index varying in at least onedirection in response to a force exerted by a muscle of the eye.
 14. Theophthalmic lens device according to claim 2, wherein said material hasan optical refractive index varying in at least one direction inresponse to a force exerted by a muscle of the eye.
 15. The ophthalmiclens device according to claim 5, wherein said material has an opticalrefractive index varying in at least one direction in response to aforce exerted by a muscle of the eye.
 16. The ophthalmic lens deviceaccording to claim 6, wherein said material has an optical refractiveindex varying in at least one direction in response to a force exertedby a muscle of the eye.
 17. The ophthalmic lens device according toclaim 1, wherein said material has an optical refractive index varyingin at least one direction in response to a force exerted by the zonulae.18. The ophthalmic lens device according to claim 2, wherein saidmaterial has an optical refractive index varying in at least onedirection in response to a force exerted by the zonulae.
 19. Theophthalmic lens device according to claim 5, wherein said material hasan optical refractive index varying in at least one direction inresponse to a force exerted by the zonulae.
 20. The ophthalmic lensdevice according to claim 6, wherein said material has an opticalrefractive index varying in at least one direction in response to aforce exerted by the zonulae.
 21. The ophthalmic lens device accordingto claim 1, wherein said material has an optical refractive indexvarying in at least one direction in response to a force exerted by aneyelid.
 22. The ophthalmic lens device according to claim 2, whereinsaid material has an optical refractive index varying in at least onedirection in response to a force exerted by an eyelid.
 23. Theophthalmic lens device according to claim 5, wherein said material hasan optical refractive index varying in at least one direction inresponse to a force exerted by an eyelid.
 24. The ophthalmic lens deviceaccording to claim 6, wherein said material has an optical refractiveindex varying in at least one direction in response to a force exertedby an eyelid.
 25. The ophthalmic lens device according to claim 1,wherein said ophthalmic lens device is a contact lens.
 26. Theophthalmic lens device according to claim 2, wherein said ophthalmiclens device is a contact lens.
 27. The ophthalmic lens device accordingto claim 5, wherein said ophthalmic lens device is a contact lens. 28.The ophthalmic lens device according to claim 6, wherein said ophthalmiclens device is a contact lens.
 29. The ophthalmic lens device accordingto claim 1, wherein said ophthalmic lens device is an intraocular lens.30. The ophthalmic lens device according to claim 2, wherein saidophthalmic lens device is an intraocular lens.
 31. The ophthalmic lensdevice according to claim 5, wherein said ophthalmic lens device is anintraocular lens.
 32. The ophthalmic lens device according to claim 6,wherein said ophthalmic lens device is an intraocular lens.
 33. Theophthalmic lens device according to claim 1, wherein said material hasportions whose orientation is responsive to force exerted by oculartissue.
 34. The ophthalmic lens device according to claim 2, whereinsaid material has portions whose orientation is responsive to forceexerted by ocular tissue.
 35. The ophthalmic lens device according toclaim 5, wherein said material has portions whose orientation isresponsive to force exerted by ocular tissue.
 36. The ophthalmic lensdevice according to claim 6, wherein said material has portions whoseorientation is responsive to force exerted by ocular tissue.